The present invention relates to microfluidic devices that have built-in means for controlling fluid flow.
This invention relates to the microfluidic devices that contain built-in means for controlling fluid flow. In one aspect of the present invention, certain sections of microfluidic channels contain porous materials that inhibit fluid flow. These sections are referred to herein as porous membrane valves. In use, when fluid encounters these regions, fluid flow will be inhibited until sufficient pressure is provided for the fluid to overcome the impedance provided by the porous materials.
In certain embodiments, these microfluidic devices consist of sandwiched stencils as in U.S. patent application Ser. No. 09/453,029. The impedance regions can be constructed within the channels in a number of ways. In a preferred embodiment, porous materials are inserted into or between channels to form the impedance region. In another preferred embodiment, the impedance region is a sheet or layer of material that forms one of the stencil layers of the device. Fluid travels through channels in one layer of a device and passes through vias (apertures between layers) that lead through the stencil layer composing the impedance region to channels on an upper or lower layer of the device. In other embodiments, an impedance region may be constructed by inserting or flowing one or more ingredients into a channel and allowing the ingredients to partially or fully solidify, such as by partial or complete evaporation. The flowing ingredient(s) from which the impedance region is constructed may be a liquid, slurry, or suspension of polymers, inorganic materials, or other materials known in the filtering art.
Multiple microfluidic valves described here can be built into a single device. The valves can have similar or very different impedances, depending on numerous factors including the composition of the materials or geometry used to construct the valves.
Definitions
The term xe2x80x9cchannelxe2x80x9d as used herein is to be interpreted in a broad sense. Thus, it is not intended to be restricted to elongated configurations where the transverse or longitudinal dimension greatly exceeds the diameter or cross-sectional dimension. Rather, such terms are meant to comprise cavities or tunnels of any desired shape or configuration through which liquids may be directed. Such a fluid cavity may, for example, comprise a flow-through cell where fluid is to be continually passed or, alternatively, a chamber for holding a specified, discrete amount of fluid for a specified amount of time. xe2x80x9cChannelsxe2x80x9d may be filled or may contain internal structures comprising valves or equivalent components.
The term xe2x80x9cmicrofluidicxe2x80x9d as used herein is to be understood, without any restriction thereto, to refer to structures or devices through which fluid(s) are capable of being passed or directed, wherein one or more of the dimensions is less than 500 microns.
The term xe2x80x9cporous membrane valvesxe2x80x9d as used herein describes a portion of, or an interface with, a microfluidic channel or element that restricts fluid flow rate for a given pressure using a porous material. A restriction of flow rate for a particular pressure may also be called an impedance. An incredibly wide variety of materials may be used to create a porous membrane valve, as would be recognized by one skilled in the art of filtering. Factors that may affect the impedance caused by a particular porous membrane valve include, but are not limited to, the following: membrane dimensions; network geometry between a membrane and associated inlet or outlet channels; membrane pore size/void volume; membrane pore geometry (for example, if pores are randomly dispersed or aligned with the direction of fluid flow); and membrane material, including any chemical interaction between the membrane and a working fluid (for example, if the membrane is composed of hydrophobic material and an aqueous solution flows in the device).